1. Field of the Invention
The present invention relates to a pressure-sensitive adhesive composition.
2. Discussion of Related Art
Light emitted from a surface of an apparatus such as a TV, a monitor, a gaming apparatus or a mobile phone has a direct influence on brightness of a screen. In addition, improving luminance of a light source is an important issue with regard to contrast. The luminance of a light source also has a direct influence on the brightness of a lighting apparatus. In addition, when the luminance of the light source is increased in an optical or lighting apparatus, a current amount to be used may be reduced.
To uniformly emit light from a light source, new light guide plates and diffuser sheets or plates are being designed, and research on the shape or arrangement of a light source such as a cold cathode-ray tube or light emitting diode, or a means for inducing emission using low power is underway. In addition, there have been attempts to improve a luminance by disposing an optical diode such as a diffuser plate or retro reflective plate above a light source or light guide plate.
In a structure of a light source such as a back light unit, generally, a diffuser plate is simply placed above a light source or light guide plate. Thus, an air gap is present between the light source or light guide plate and the diffuser plate. The air gap induces the loss of emitted light. Accordingly, there have been attempts to give a diffusion function through surface treatment to the light guide plate, or remove the air gap using matching oil.
However, during the process of giving the diffusion function to the light guide plate, process efficiency is greatly decreased and it is difficult to coordinate with a change in product size. When the matching oil is used, liquid leakage also occurs due to heat of the light source itself.
As the diffuser plate, a hard-type material, for example, based on poly(methyl methacrylate) (PMMA) or polycarbonate (PC) is used. However, the material curls easily under severe conditions such as high temperature or high temperature and humidity conditions, and has a limit in its application to manufacture of a flexible device. Moreover, a plastic material releases moisture, a solvent or other liquid additives contained therein in a gas state, which is generally called “out-gassing.” Due to such a phenomenon, the released gas generates bubbles and thus induces degradation in optical properties.